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Heat Capacity and Calorimetry

AP Chemistry· difficulty 4/5

A 1.250 g sample of octane (C8H18C_8H_{18}, M = 114.23 g/mol) is burned in a bomb calorimeter with heat capacity 8.93 kJ/∘^\circC. Temperature rises from 24.62∘^\circC to 30.57∘^\circC. What is ΔU\Delta U per mole of octane?

  • A

    −5470-5470 kJ/mol

  • B

    −4860-4860 kJ/mol

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  • C

    −3920-3920 kJ/mol

  • D

    −2780-2780 kJ/mol

Explanation

qq = CΔTC\Delta T = (8.93)(5.95) = 53.13 kJ released. Mol octane = 1.250/114.23 = 0.01094. ΔU\Delta U = −53.13-53.13/0.01094 = −4856-4856 ≈−4860\approx -4860 kJ/mol.

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